Recent innovations in ramp generators for pulse width modulators employ a first symmetrical dual ramp generator for generating first and second ramps having a predetermined voltage range and extending for a period equal to or greater than one half the clock cycle. The comparator device responds to each of the first and second symmetrical ramps and to a reference level within the predetermined voltage range of the first and second ramps for generating corresponding first and second asymmetrical drive signals. A second symmetrical dual ramp generator responds to the first and second asymmetrical drive signals for generating third and fourth asymmetrical overlapping ramps which extend beyond the predetermined voltage range. The problem of calibration is compounded in such systems because the two sets of ramps have different durations yet they must have identical slopes. Further, when the first set of ramps are calibrated they must be set to swing the same voltage range as the usable range of the second set of ramps.